a) Field of the Invention
This invention generally relates to picture frames and, more particularly, to corner clamp assemblies used to secure together individual frame members along a miter joint.
b) Description of the Prior Art
A common type of commercially available picture frame includes frame sections formed from extruded metal, usually aluminum. Each frame section includes longitudinal receiving channels which are accessible from the ends and back of the frame section. The frame sections are connected to each other (end-to-end) to form a rectangular frame using a corner clamp assembly located at each corner of the frame.
As shown in FIGS. 1 and 2, labeled PRIOR ART (and described in greater detail below), a conventional corner clamp assembly includes two L-shaped metal plates (an upper screw-plate and a lower backing-plate), each having two xe2x80x9clegsxe2x80x9d (forming the L-shape). Each leg of each plate is inserted into the receiving channel of a frame section, so that the plates are positioned across a miter joint. One L-shaped plate includes two-threaded openings, one in each leg. Each threaded opening is adapted to receive a threaded set-screw. When the top and bottom L-shaped plates are positioned within the channels of two adjacent frame sections, advancing the set-screws of the upper L-shaped plate causes a lower end of each screw to contact the backing L-shaped plate, forcing the two L-shaped plates to move away from each other. The separation force generated by the advanced set-screws causes the two L-shaped plates to effectively jam within the extruded frame channels, clamping the two adjacent frame members together.
Although this type of conventional corner clamp is generally effective in securing frame sections together, conventional clamps are made up of two separate elements that must be assembled within the appropriate channel of each frame section to assemble the picture frame. This clamp-assembly operation is time consuming. Also, because each conventional corner clamp assembly includes two separate and different elements, some difficulty arises in keeping track of each element prior to use (i.e., inventory) and during the assembly of a picture frame. Framers must first match both elements of each corner clamp to be used and then assemble the separate pieces into each receiving channel of two adjacent frame sections. Although, this matching and assembly procedure may require only a minute or so for each corner clamp, the professional framer will lose a substantial amount of collective assembly time when assembling hundreds of corner clamps a day.
Another problem associated with the above-described prior art is that the clamp, although providing a tremendous amount of transverse (separation) force to hold two adjacent picture frames tightly together, fails to introduce any effective lateral force to help hold each frame section in alignment along their abutting miter joint, prior to, and during securement of the clamp in the channel. The clamp elements can easily fall out of the frame section during assembly.
It is not uncommon for the framer to improperly cut a miter joint of a frame section, resulting in an assembled picture frame that includes a slight gap along one or more corners. This gap is readily noticeable because it generally exposes a portion of the relatively bright aluminum metal located under the colored paint layer. In addition to a miter gap being formed during the assembly of a picture frame, another assembly-related problem is that since the prior art corner clamps offer only a loose lateral fit when positioned within a receiving channel prior to being secured within the channel, the inserted corner clamp may shift laterally with respect to the frame sections. This lateral shifting may result in one frame section becoming offset or misaligned with respect to the other. As illustrated in FIGS. 1 and 2, labeled PRIOR ART, misalignment of frame sections results in one frame section extending beyond the other frame section at the miter joint, again exposing a portion of the bare metal of the frame section.
U.S. Pat. No. 4,694,598 issued to Eisenloffel discloses a compression clamp for securing two adjacent picture frame sections together across a miter joint. The clamp of U.S. Pat. No. 4,694,598, which is sized and shaped to fit within appropriate channels located in the frame section, includes a flat L-shaped plate having a threaded opening in each leg for receiving a threaded screw. Adjacent to each threaded opening of each leg are transverse opposing arms which are bent around each leg to form a structure that is generally rectangular in cross section. Each arm includes an arm-end that is curved upwardly towards a lower end of the screw so that as the screw is tightened, the arm-ends are forced downwardly which causes the arm structure to deform and expand within the channel of the frame section. As the screws of the compression clamp of U.S. Pat. No. 4,694,598 are tightened, the clamp will generate both transverse and lateral forces which help bind each leg of the clamp within the respective channels of each frame section. The clamp of U.S. Pat. No. 4,694,598 introduces no lateral force to the frame sections when the clamp is first inserted within the channel of the frame sections, but only when the screws are being tightened and the clamp is already binding within the channels. The lateral forces generated by the clamp of U.S. Pat. No. 4,694,598 may actually cause one frame section to become misaligned with respect to the other frame section, as the screws are tightened.
U.S. Pat. No. 5.423,626 issued to Peters discloses a clamping assembly for securing two adjacent frame sections together across a miter joint, including two L-shaped plates. One plate has threaded openings that receive screws, while the other plate has recesses that are slightly offset with respect to the threaded openings. The two plates are positioned against each other and inserted into appropriate channels of each frame section. As the screws are tightened, their lower ends enter the offset recesses which causes the two plates to move transversely apart from each other and simultaneously shift laterally within the channel of each frame section.
The clamp assembly of U.S. Pat. No. 5,423.626 is similar to the clamp assembly of U.S. Pat. No. 4,694,598 in that both clamp assemblies introduce laterally directed forces to the frame sections only when the screws are tightened and the clamp binds within the channels of the frame sections.
It would be beneficial to provide a clamp assembly for use with picture frames which introduces a lateral force to the frame sections upon insertion into appropriate channels of the frame sections.
Accordingly, it is an object of the present invention to provide a corner clamp assembly that generates both transverse and lateral clamping forces which are useful in holding the individual frame members of a picture frame together which overcomes the deficiencies of the prior art.
Another object of the invention is to provide a corner clamp for securing individual frame members together which is inexpensive to manufacture and easy to use.
Another object of the invention is to provide a corner clamp for securing individual frame members together which generates a lateral force independent of any transverse force generated.
Another object of the invention is to provide a corner clamp for securing individual frame members together which is easier and faster to install than prior art clamps.
An improved picture frame corner clamp assembly includes an L-shaped screw plate and an L-shaped backing plate. According to the invention, both plates are elastically secured to each other by an elastic member, resulting in an L-shaped corner clamp assembly preferably having the screw plate shifted slightly with respect to the backing plate. The screw plate and the backing plate each include two legs. Each of these legs is sized to fit within a receiving channel of a picture frame section. The magnitude of offset between the screw plate and the backing plate is preferably such that the sum of this offset distance and the width of the legs is equal to or larger than the width of the receiving channel. This arrangement ensures that upon insertion into the receiving channel of a frame section, the screw plate will become biased against an inside wall of the receiving channel, while the backing plate will become biased against an opposing (outer) wall of the receiving channel, due to the spring action of the elastic member connecting the two plates together. The result is that each frame section is urged into tight engagement and alignment with the legs of the clamp assembly, ensuring that adjacent frame sections are secured and properly aligned with each other along their mitered edges.